Effects of Neem Seed Extract on Nitrate and Oxalate Contents in Amaranth Fertilized with Mineral Fertilizer and Cricket Frass

Abstract

A vegetable’s high antinutrients, nitrate (NO3−) and oxalate, could be remediated by neem seed extract. The combined use of neem seed extract with mineral fertilizer and cricket frass was conducted to evaluate their effects on amaranth’s tissue NO3− and oxalic acid contents by inhibiting nitrification. The effects of five soil amendments were investigated: unamended, mineral fertilizer, and three rates of cricket frass (3.125 Mg ha−1, 6.25 Mg ha−1, and 12.5 Mg ha−1), combined with two rates of neem seed extract: without (−Nm) and with (+Nm) extract. Only the neem extract applied to soils receiving mineral fertilizers decreased soil tissue NO3−−N contents (0.82 g kg−1 for −Nm vs. 0.62 g kg−1 for +Nm). The oxalic acid content of amaranth decreased with mineral fertilizer (0.60 and 0.46 g kg−1 for −Nm and +Nm, respectively), yet increased with the higher rates of cricket frass (1.42–1.52 g kg−1 for −Nm, and 1.23–1.51 g kg−1 for +Nm) compared to the unamended soil (1.05 and 1.00 g kg−1 for −Nm and +Nm). Cations, including K, Ca, Mg, and Na derived from cricket frass, may enhance biosynthesis and the accumulation of oxalic acid. The neem seed extract decreased the tissue’s oxalic contents regardless of soil amendments.